Low loss ferrite power circulator operating as a power combiner or power divider



1966 O.J. DIGIONDOMENICO ETAL 3,277,400

LOW LOSS FERRITE POWER CIRCULATOR OPERATING AS A POWER COMBINER OR POWER DIVIDER Filed April 27, 1964 6 6. & mm J w? w Mi mi 7 f 6 OMZV A f M MWIM W WWW W M? y mm m W Z 0 w Q cu m g M [L 6%,

United States Patent 3,277,400 LOW LOSS FERRITE POWER CIRCULATOR OPER- ATING AS A POWER COMBINER 0R POWER DIVIDER Oresto J. Digiondomenico, Baltimore, John A. Geikler, Jr., Linthicum Heights, and Tommy S. Weaver, Glen Burnie, Md., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Apr. 27, 1964, Ser. No. 363,028 6 Claims. (Cl. 333-11) The present invention relates to a circulator and more particularly to a three port ring circulator that can be used either as a power combiner or a power divider.

It is frequently necessary to transfer, combine, or divide electromagnetic energy in various portions of equipment. While various means of accomplishing this transfer have been utilized, many of the more successful devices operating in the microwave spectrum employ an element of nonreciprocal material such as ferrite. This material is disposed in one or more sections of waveguides so that the microwave energy will be propagated therethrough. By creating a magnetic fiux field through this element there will be a gyromagnetic effect which may be effectively utilized to control the microwave energy in the desired manner.

The present invention utilizes nonreciprocal material to provide a device wherein power from either of two input ports can be delivered to a third or output port without any resulting 3 db loss. It is known that nonreciprocal circuit elements can be realized at microwave frequencies by utilizing the ferromagnetic Faraday rotation in ferrite. Also, another way of constructing a nonreciprocal element has been found-that, as in the case of the Faraday rotation, depends on the fact that, in the presence of a static magnetic field, the permeability of a ferrite is a nonsymmetrical tensor. As a result, if a rectangular waveguide is partially filled with ferrite in an asymmetrical manner, and a static magnetic field is applied transversely, the propagation constants of the modes will depend on the direction of propagation. A theoretical discussion of this is given in an article entitled A Nonreciprocal Microwave Component by M. L. Kales et al. published in the Journal of Applied Physics, volume 24, pages 816-817, June 1953.

The present invention has an advantage over heretofore known devices, such as T junctions, 3 db couplers and hybrid rings, as these devices have at least a 3 db loss between ports, while the present invention delivers power without this 3 db loss.

It istherefor a general object of the present invention to provide a power combiner which is capable of delivering power with a minimum of loss.

Another object of the present invention is to provide a three port device that can be used as a power combiner or as a power splitter.

Still another object of the present invention is to provide a relatively simple nonreciprocal waveguide junction that has low power loss.

Other objects and advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIGURES 1(a) and 1(1)) show devices of the prior art that use ferrite material to direct the path of transmission of electromagnetic waves;

FIGURE 2 is a diagrammatic view showing the present invention being used as a power combiner;

FIGURE 3 is diagrammatic view showing the present invention being used as a power divider;

FIGURE 4 is a diagrammatic view showing the required phase shifts between ports; and

FIGURE 5 is a perspective view showing a ferrite circulator.

Referring first to the devices of the prior art, FIGURE 1(a) shows a ferrite Y circulator 11 having three ports A, B, and C. A piece of ferrite is placed at the junction of the three ports and is used to direct the path of power entering the various ports. Power in at A exits at B; power in at B exits at C; and power in at C exits at A. By reversing the magnetizing field, the device can be utilized as a switch.

Referring now to FIGURE 1(b) of the drawing, there is shown a re-entrant wave-guiding structure 12 defining a closed loop path for wave energy within it. The structure is rectangular in cross section and a strip of ferrite material is placed within the wave-guide structure and offset from the center. A steady magnetic field is applied to the ferrite material in the direction perpendicular to its length and perpendicular to its shortest dimension, i.e., in a direction parallel with the axis of the closed loop. Three ports A, B, and C are provided and compression Wave energy entering the structure by way of the A port emerges at B port; energy entering by way of the B port emerges at the C port; and energy entering at the C port emerges at the A port.

In FIGURE 2 of the drawing there is shown a three port ring power combiner 13 capable of delivering power from either or both of two input ports C and D to a third or output port E without the customary 3 db loss. I

-let power be applied at port C. In order to transmit the energy from port C to port E, it is necessary that the I phase shift of a wave traveling in a clockwise direction from port C either be equal to the phase shift of a wave traveling in a counterclockwise direction or that the difference between the two phase shifts be a whole number of full wavelengths. The following equation sets forth this relationship:

where CE is the phase shift between ports C and E, taken in a clockwise direction, as shown in FIGURE 4; CD is the phase shift between ports C and D, taken in a counterclockwise direction; DE is the phase shift between ports D and E taken in a counterclockwise direction; and m is equal to zero or any integer.

In order to achieve isolation at port D, it is necessary that the energy traveling in a counterclockwise direction between ports C and D arrive degrees, or an odd integer multiple thereof, out of phase with the energy traveling in a clockwise direction between ports C and D. The following equation shows this relationship:

where CD is the phase shift between ports C and D, taken in a counterclockwise direction; CE is the phase shift between ports C and E taken in a clockwise direction; ED is the phase shift between ports E and D, taken in a clockwise direction; and n is equal to zero or any integer.

In order to transmit energy from port D to port E, it is necessary thatthe phase shift of a wave traveling in a clockwise direction from port D either be equal to the phase shift of a wave traveling in a counter clockwise direction or that the difference between the two phase shifts be a whole number of full wavelengths. equation sets forth this relationship:

where qbDE is the phase shift between ports D and E; taken in a counterclockwise direction; DC is the phase shift between ports D and C, taken in a clockwise direction; CE is the phase shift between ports C and E, taken in a clockwise direction; and m is equal to zero or any integer.

In order to achieve isolation at port C, it is necessary that the energy traveling in a counterclockwise direction between ports D and C arrive 180 degrees, or an odd integer multiple thereof, out of phase with the energy traveling in a clockwise direction between ports D and C. The equation for this relationship is:

where DC is the phase shift between ports D and C, taken in a clockwise direction; DE is the phase shift between ports D and E, taken in a counterclockwise direction; EC is the phase shift between ports E and C taken in a counterclockwise direction; and n is equal to zero or any integer.

By combining Equations 1 and 2, then: (5) DE+ED=(2m+2n+l)1r by combining Equations 1 and 3, then:

( CD+DC=4m1r and by combining Equations 1, 4, and 6, then:

(7) CE+EC: (2m-[-2n+1)1r As in and It may assume an infinite number of values, there will, therefore, be an infinite number of solutions. However, as the combiner becomes more frequency sensitive as m and 11 increase, the optimum design will be where m=n=0. Accordingly, by using a value of zero for m and n, and by algebraic manipulation Equations 4, 5, 6, and 7 become:

The following By combining Equations 8 and 10 and eliminating the negative sign before 1r, as the equations are symmetrical, and by also eliminating the negative signs in Equations 9, 10, and 11 the following Working equations are obtained:

As a working parameter, the values of CD, DE, and (PEG are set equal and, therefore, from Equation 12, it can be seen that:

By substituting the value of DE=60 into Equation 13, then it can be seen that:

or i

By substituting the value of CD=60 into Equation 14, the value of DC is:

By substituting the value of EC=60 into Equation 15, then:

As best shown in FIGURE 5 of the drawing, magnetic fields are applied to the ferrites. The position and construction of the ferrite strips and the strength of the magnetic fields determine the two different phase velocities within each sector of the waveguide for waves progressing in opposite directions. The magnetic fields might be applied in any well-known manner such as, for example, by an electromagnet as shown in U.S. Patent 2,794,- 172, which issued May 28, 1957, to W. E. Kock.

In operation, assuming the device of the present invention is being used as a power combiner, as shown in FIGURE 2 of the drawing, power will be applied at ports C and D and will exit at port E. A wave traveling clockwise from port C to port E will be phase shifted CE or degrees. The wave traveling in a counterclockwise direction from port C to port D to port E will be phase shifted CD+DE, which is a total of 120 degrees. Thus the two waves will arrive at port E in phase and therefore energy will be delivered to port E. On the other hand, isolation will be encountered at port D. The wave traveling in a clockwise direction from port C to port E to port D will be phase shifted CE+ ED or 240. The wave traveling in a counterclockwise direction from port C to port D will be phase shifted CD or 60. Thus it can be seen that the two waves will arrive at port D 180 degrees out of phase and this phase difference *will cause cancellation, and isolation of port D will be achieved.

Likewise, a similar result is achieved when power is applied at port D. A wave traveling clockwise from port D to port C to port E will be phase shifted 420 and a wave traveling counterclockwise from D to B will be phase shifted 60 degrees. The difference between these two phase shifts is 360 degrees and, therefore, the energy will be delivered at port E. A wave traveling clockwise from port D to port C will be phase shifted 300 degrees and a wave traveling counterclockwise from port D to port E to port C will be phase shifted 120 degrees. Again it can be seen that the two waves will arrive at port C 180 degrees out of phase, and this phase difference will cause cancellation, and isolation of port D will be achieved.

When the device is operating as a power divider, as illustrated in FIGURE 3 of the drawing, power is applied to port E and is divided between ports C and D. The phase shift between ports E and D is 120 degrees and also the phase shift between ports E to C to D is 120 degrees and thus energy will be delivered to port D. Likewise the phase shift between ports E and C is 60 degrees and the phase shift between ports E to D to C is 420 degrees. Thus as the difference is 360 degrees, energy will also be delivered at port C.

It can therefore be seen that the present invention provides an improved three port circulator that can be used either as a power combiner or a power divider without the customary 3 db loss between ports that is normally associated with such devices. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. For example, although ferrite has been specifically mentioned as a material for providing the desired phase shifts, any magnetically polarizable material capable of exhibiting gyromagnetic properties can be used equally as Well. One such material is yttrium-iron-alurninum garnet, which is disclosed in U.S. Patent 3,101,456, which issued August 20, 1963, to Julian Brown et al. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A microwave circulator comprising:

a circular waveguide structure having a closed loop path for electromagnetic energy and having first and second input ports and an output port each communicating with said closed loop path, and

means for phase shifting electromagnetic wave energy applied at said first and second input ports, the degree of phase shift of an electromagnetic wave traveling in a counterclockwise direction between said first and second input ports, between said second input port and said output port, and between said output port and said first input port being equal, the degree of phase shift of an electromagnetic wave traveling in a clockwise direction between said first input port and said output port being equal to the degree of phase shift between said output port and said second input port and greater than the degree of phase shift between adjacent ports of an electropath for electromagnetic energy and having first and second input ports and an output port each communicating with said closed loop path, and

means for phase shifting electromagnetic wave energy applied at said first and second input ports, the degree of phase shift of an electromagnetic wave traveling in a counterclockwise direction between said first and second input ports, between said second input port and said output port, and between said output port and said first input port each being 60 degrees, the degree of phase shift of an electromagnetic wave traveling in a clockwise direction between said first input port and said output port being 120 degrees, the degree of phase shift of an electromagnetic wave traveling in a clockwise direction between said output port and said second input port being 120 degrees, and the degree of phase shift of an electromagnetic wave traveling in a clockwise direction between said input ports being 300 degrees, whereby energy entering said first and second input ports will be combined at said output port and each said input port will be isolated from the other said input port.

magnetic wave traveling in a counterclockwise direction, and the degree of phase shift of an electromagnetic wave traveling in a clockwise direction between said input ports being greater than the degree of phase shift of an electromagnetic wave traveling in a clockwise direction between said output port and said second input port whereby energy entering said first and second input ports will be combined at said output port and each said input port will be isolated from the other said input port.

2. A microwave circulator as set forth in claim 1 wherein said means for phase shifting comprises:

first, second, and third members of magnetically polarizable material located within said circular waveguide structure, said first member being located between said first and second input ports, said second member being located between said second input port and said output port, and said third member being located between said first input port and said output port, and

means for separately magnetizing said first, second, and

third members.

5. A microwave circulator as set forth in claim 4 wherein said means for phase shifting comprises:

first, second, and third members of magnetically polarizable material located within said circular waveguide structure, said first member being located between said first and second input ports, said second member being located between said second input port and said output port, and said third member being located between said first input port and said output port, and means for separately magnetizing said first, second, and third members.

6. A microwave circulator as set forth in claim 5 wherein said first, second, and third members are of ferrite material.

References Cited by the Examiner 3. A microwave circulator as set forth in claim 2 wherein said first, second, and third members are of ferrite material.

4. A microwave circulator comprising:

a circular waveguide structure having a closed loop IRE, August 1960, pp. 1497, 1498.

HERMAN KARL SAALBACH, Primary Examiner.

P. L. GENSLER, Assistant Examiner. 

1. A MICROWAVE CIRCULATOR COMPRISING: A CIRCULAR WAVEGUIDE STRUCTURE HAVING A CLOSED LOOP PATH FOR ELECTROMAGNETIC ENERGY AND HAVING FIRST AND SECOND INPUT PORTS AND AN OUTPUT PORT EACH COMMUNICATING WITH SAID CLOSED LOOP PATH, AND MEANS FOR PHASE SHIFTING ELECTROMAGNETIC WAVE ENERGY APPLIED AT SAID FIRST AND SECOND INPUT PORTS, THE DEGREE OF PHASE SHIFT OF AN ELECTROMAGNETIC WAVE TRAVELING IN A COUNTERCLOCKWISE DIRECTION BETWEEN SAID FIRST AND SECOND INPUT PORTS, BETWEEN SAID SECOND INPUT PORT AND SAID OUTPUT PORT, AND BETWEEN SAID OUTPUT PORT AND SAID FIRST INPUT PORT BEING EQUAL, THE DEGREE OF PHASE SHIFT ON AN ELECTROMAGNETIC WAVE TRAVELING IN A CLOCKWISE DIRECTION BETWEEN SAID FIRST INPUT PORT AND SAID OUTPUT PORT BEING EQUAL TO THE DEGREE OF PHASE SHIFT BETWEEN SAID OUTPUT PORT AND 